Selecting parameters and limits for equipment operational qualification

While operational qualification (OQ) is a well-established term within equipment qualification, users of equipment often become unsure when it comes to implementation. The biggest problem is how to select procedures and acceptance criteria. Should these be the vendor's specifications or should the users define their own limits, and, if so, how? Should all instruments of the same type have the same values or should these be optimized for each individual instrument? This article will provide an overall strategy and specific examples for HPLC on how to select procedures and acceptance limits that are based on efficient use of resources, on practicality and on the intended use of the equipment.     

Voltammetric Characterization of Micro‐ and Submicrometer‐Electrode Arrays of Conical Shape for Electroanalytical Use

Densely packed micro‐ and submicrometer electrode arrays of platinum and gold (the nominal number, N, of electrodes in each array varies between 225 and 3600) are fabricated by photolithographic technique and vapor deposition processes of metal films. The electrodes are conical‐shaped and only their apexes are exposed to the electrolytic solution. The electrode arrays are characterized electrochemically in Ru(NH₃)₆Cl₃ aqueous solutions by using cyclic voltammetry at low scan rates, to establish the number of electrochemically active electrodes (N_ac) in each array; the geometric characterization is performed by scanning electron microscopy. All the investigated arrays provide steady‐state voltammograms, indicating diffusionally independent behavior of each microelectrode. The number of microelectrodes that are active in the fabricated arrays depends on microelectrode density. In particular, for the arrays with N=3600 and N=225, the fraction of active sites is about 45% and 90%, respectively. The analytical performance of some of the Pt version of the arrays is tested in hydrogen peroxide solutions, allowing verifying that linear calibration plots over the concentration range (0.1–20 mM) are obtained. This dynamic range is larger than that typically recorded at smooth polycrystalline platinum electrodes (0.5–5 mM), and the better performance is attributed to both the higher aspect ratio of the cone geometry and the higher mass transport associated to each microelectrode of the array. Reproducibility (within 3.5%, r.s.d.) and long‐term stability (within 5%, r.s.d., after 8 h continuous use) of the electrode systems are satisfactory. A low detection limit, based on the signal to noise ratio equal to 3, of 0.05 mM is found, which is adequate for a rapid monitoring of H₂O₂ in real samples and industrial processes.     

Electron-density-dependent fused-sphere surfaces derived from pseudopotential calculations

Fused-sphere surfaces can be used to mimic a molecular boundary associated with a constant value of the electron density. The simplest of such fused-sphere models are constructed by using the atomic radii for the spherical isodensity surfaces of individual atoms. In this work, we discuss the extension of this model to molecules containing atoms beyond the second row. In these many- electron systems, the computation of electron densities is usually simplified by adopting a pseudopotential (or effective-core potential) approach. Here, we discuss the performance of large- and small-core pseudo-potential calculations as a tool to derive atomic radii. Our results provide an optimum set of variable radii that can be used to build fused-sphere surfaces. This continuum of surfaces provides a simple approximation to the low-electron-density regions around molecules with heavy atoms.     

ZnO微晶的水热合成及形貌控制研究

以Zn(NH3)4(Ac)2为前驱体,不加任何模板剂和表面活性剂,低温下通过改变反应条件(如前驱体浓度、反应时间及反应温度),实现了对ZnO微晶形貌和尺度的有效控制.所得花状、蜂窝状、柱状ZnO用X射线衍射仪和扫描电镜进行了鉴定和表征,并初步探讨了不同形貌ZnO微晶的生长机理.     

Selection of terms for a CI wavefunction to preserve potential surface features

A cumulative selection procedure for choosing configuration functions for inclusion in CI calculations is described. The objective of the method is to obtain equal energy loss, relative to unselected calculations, for different states and different regions of the potential surface. Results obtained from calculations on the BH molecule indicate an overall advantage in comparison to the threshold selection procedure, particularly with regard to molecular geometry changes.     

离散小波变换-遗传算法-交互检验法用于近红外光谱数据的高倍压缩与变量筛选

用遗传算法(GA)与交互检验(CV)相结合建立了一种用于对近红外光谱(NIR)数据及其离散小波变换(DWT)系数进行变量筛选的方法，并应用于烟草样品中总挥发碱和总氮的同时测定。结果表明：NIR数据经DWT压缩为原始大小的3．3％时基本没有光谱信息的丢失；有效的变量筛选可以极大地减少模型中的变量个数，降低模型的复杂程度，改善预测的准确度。     

Molecular-shape recognition of polycyclic aromatic hydrocarbons in reversed phase liquid chromatography

Summary The molecular-shape recognition of polycyclic aromatic hydrocarbons has been studied on various stationary phases in reversed-phase high-performance liquid chromatography. The examined stationary phases were phenyl-, diphenyl-, triphenyl- and benzyl-bonded silicas. The results of regression analysis inidcated that triphenylsilica is the best packing material to recognize the difference in the molecular-shape of structural isomers. This fact was confirmed by the separation of 4-ring isomers.     

前驱体水解对纳米铂形状控制合成的影响

以聚丙烯酸钠(NaPA: M_w ≈ 2100)为保护剂，对比研究了H_2还原K_2PtCl_4 和K_2PtCl_6水溶液制备纳米铂晶粒的形状选择性，揭示了前驱体的水解对纳米铂 晶粒的形状控制合成具有显著影响。文献中通常采用的合成立方形状纳米铂的 K_2PtCl_4前驱体在水溶液中不稳定，避光静置一周会析出黑色沉淀。这种不稳定 性导致了以K_2PtCl_4为Pt前驱体的合成结果难以重复。相比而言，避光静墨的 K_2PtCl_6水溶液很稳定，以它为前驱体合成的纳米铂通常为削角八面体。 K_2PtCl_6水溶液暴露于室内光线中会出现[PtCl_6]~(-2)的光致水解。当[PtCl_6] ~(2-)的紫外特征吸收峰(260nm)由于光致水解完全消失后，以聚丙烯酸钠为保护剂 ，通过H_2还原可以有选择性地(约80%)合成由{100}晶面包裹的立方体形状的纳米 铂。